Method of making arsenate of lead



'0. F. HEDENBURG AND D.'S. PRATT. METHOD OF MAKING ARSENATE 0F LEAD.

APPLICATION FILED JULY I, 1919.

1,344,035. Patented June 22, 1920.

V? W (June-tow;

UNITED STATES A PATENT OFFICE.

OSCAR F. HEDENBURG AND DAVID S. PRATT, OF PITTSBURGH, PENNSYLVANIA,

ASSIGNORS TO THE TOLEDO REX SPRAY COMPANY, OF TOLEDO, OHIO, A CORPO- RATION OF OHIO.

METHOD OF MAKING ARSENATE OF LEAD.

Specification of Letters Patent. Patented J ne 22, 1920 Applicatlon'filed July 1, 1919. Serial No. 307,986.

To all whom it may concern:

Be it known that we, OSCAR F. HEDEN- BURG and DAVID S. PRATT, citizens of the following to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same a,

This invention relates to the production of arsenate of lead, and particularly to a method of combining lead oxid with arsenic acid or arsenic oxid in an expeditious, economical and effective manner to produce an arsenate having improved properties and particularly adapted for utilization in the production of insecticides.

'A particular object of the invention is the production of arsenate of lead in a state of extreme sub-division, substantially free from electrolytes such as nitric acid or soluble salts, e. 9., lead nitrate or lead salts other than arsenates, the arsenate being thus available for uses where the presence of an electrolyte is detrimental.

Further objects and advantages of our invention Will be apparent from the following specification, when read in connection with the accompanying drawing illustrating diagrammatically an apparatus adapted for use in the practice thereof.

Thearseriate of lead produced in accordance with the method hereinafter described, is particularly adapted for use, in connection with a deflocculating agent, as an insecticide, as described and claimed in our application, Serial No. 307985 filed of even date herewith. The arsenate is, however, available for other purposes.

It has been heretofore proposed to produce arsenate of lead by the combination of lead oxid and arsenic acid in the presence of an electrolyte, such as nitric acid or acetic acid. The arse'nate produced in this manner is not, however, without special purification or treatment, as well adapted for use in connection with a deflocculating agent, as described in our said application, since the dispersing or deflocculating effect of such agent is partially overcome by the presence of the electrolyte. Furthermore,

the yield of arsenate is somewhat decreased by the presence of the electrolyte, which acts as a solvent of the lead arsenate.

In carrying out our invention we produce normal or acid arsenate of lead without re-' course to other dissolving agents by directly [combining finely divided lead oxid, such,

for example, as yellow sublimed or fumed lead oxid, or litharge, with arsenic acid or arsenic oxid under carefully regulated eonditions as to temperature, concentration and rate of addition of the arsenic acid or oxid to a suspension of the lead oxid.

'Either arsenic acid or arsenic oxid will readily dissolve in water to form a solution of arsenic acid. Preferably the finely divided lead oxid is suspended in a liquid medium which is maintained at the proper temperature while the arsenic acid or oxid, in solution of appropriate concentration, is

slowly added, the whole being agitated throughout the reaction. to insure proper suspension and intimate commingling and reaction of the materials. The temperature, concentration and other factors as set forth 'in the following description, are those which we have found to be most desirable for the production of lead arsenate of improved properties in a fine crystalline condition and free from electrolytes and with slightly increased yields.

As an example of the practical applicapounds of dried arsenate of lead. About 2700 gallons of water are placed in a tank or other suitable receptacle provided with agitating means and the water is heated to a temperature of about 70 C. to 100 C. by

steam or other suitable heating means. The

character of the product will vary somewhat with the particular temperature employed. Preferably the steam is conducted into the water through a ,pipe disposed about the bottom and when the temperature has reached that specified, agitation is c0111 .menced through the operation of a. me-

tion of our invention, we will describe the production of a batch of substantially 2500 enters the tank. Agitation ot the lead oxid in the water is continued for about 15 min utes, or until a thorough suspension is assured, and a partial solution or hydrolysis of the lead oxid is accomplished, thereby giving the solution an alkaline reaction.

The arsenic acid or oxid is preferably added in the form of a solution which is previously prepared in a suitable receptacle: for example, 200 pounds of concentrated arsenic acid solution, Varying from about 58 Be, containing about 55% of As O to about 09.5 156, containing about 62.5% of As O is mixed in the receptacle with water to make about 30 gallons of the solution. The acid solution is permitted to flow into the tank containin the suspended lead oxid at a regulated rate requiring about 45 minutes for the contents of the receptacle to enter the tank. Two receptacles are preferably employed, in one of which an additional quantity of the similarly diluted ar senic acid solution "is prepared while the other is being discharged. As soon as the first receptacle is empty, the second is started to deliver its contents, so that a continuous stream of arsenic acid solution is provided until the desired reaction is completed. The result of this step of adding the arsenic acid or oxid gradually, together with thorough agitation, is that the suspending medium retains its alkaline reaction until approximately 50% of the total arsenic acid or oXid has been added. Fur thermore, as generally carried on an acid reaction does not appear in the suspending medium until approximately 90% of the arsenic acid or oxid has been added.

Theoretically, an amount of arsenic acid equivalent to about 825 lbs; ofarsenic oxid should be required to convert 1600 pounds of lead oXid into acid lead arsenate. It is not, however, desirable to add the calculated amount of arsenic acid, since practical experience has demonstrated that acid lead arsenate produced by the method herein de scribed contains from about 31.5 to about 32.5% of As O instead of 33.13%, the theoretical content. Consequently, a saving in the arsenic acid solution maybe accomplished by estimating roughly when 85 to 90% of the required arsenic acid solution has been added and then testing the supernatant liquor for an excess thereof by means of a neutral lead solution. Small amounts of the arsenic acid solution are then added. as required, and the process continued until the test with lead solution indicates the presence of uncombined arsenic acid.

acid, agitation is stopped and the precipitate allowed to settle. When settling is fairly complete, the supernatant liquor is withdrawn and enough water is added tovmake a volume of about 5500 gallons. Agitation is again commenced and the precipitate thereby thoroughly washed. When the washing is completed the precipitate is permitted to settle and the supernatant liquor withdrawn. The material may then be pumped to a filter press or other suitable device for separating the arsenate from the liquor, after which the lead arsenate may be made into a paste, or may be thoroughly dried in a suitable drier.

The state of sub-division of the lead oxid employed in our method is an important factor. The particles of the coarser varieties of litharge when treated in the manner described, become coated with arsenate which retards the further combination thereof with the arsenic acid.. Sublimed or fumed lead oxid, containing98% up to 100% of lead oxid, is, however, of such fineness that it can be converted into lead arsenate with substantial completeness according to the process of the present invention. Air floated lead oxid can also be employed. The temperature maintained and the concentration and rate of addition of the arsenic acid, are also important, and while some variation is possible, we have found the btst results to be produced when the methodherein described is followed.

In the accompanying drawing various portions of the apparatus are illustrated as arranged on separate floors to permit convenient handling of the materials. Thus, we provide, on the first floor, a striking tank, 2, of suitable capacity and having outlets 3 disposed at diilerent levels, and communieating with a drain pipe 4. Valves 5 control the individual outlets, permitting withdrawal of the liquor after settling as previously described. The tank 2 is pro vided with a rotating or other form of agitator, 6, and is arranged to receive the lead oxid and arsenic solution, through the chute 8 and pipe 7, respectively, from the floor above. The tank 2 is heated by steam delivered through a pipe, 9, disposed within the tank and provided with perforations through which the steam issues and is directed against the bottom, toward the center, and upwardly in the tank. The agitator 6 may be driven through a bevel gear 10 and pinion 11 from a-shaft 12, which is in turn driven by a motor 13 or any other source of power.

A hopper 14.- is provided at the upper end of the chute 8 to receive the lead oXid and a sitter comprising revolving brushes over a screen 15, is disposed in the hopper and is driven by a belt 16 from the shaft 12. The sifter may be constructed of wire mesh, preferably having 20 meshes to the inch, thus insuring a proper sub-division of the lead oxld. A tub 17 having a capacity of about 30 gallons, is preferably supported on a floor. A pipe 21 conveys the material from fihe pump 20 to a filter press 22, on the first oor.

The filter' press may be of the usual design and constructed to deliver the filtrate to a launder 23. The pressure gage 24 is provided in the inlet to the filter press. When the gage indicates a pressure of forty pounds or more, the press will be full and the cakes of a still", solid consistency.

A hopper 25, is provided beneath the filter press, 22, to receive the cake when the press is opened. A worm conveyor 26 on the bottom and preferably driven from the shaft 12 churns the cake into a mass of uniform consistency and delivers it through an outlet 27. The arsenate of lead may be utilized in this condition, or may be dried in any suitable dryin device or apparatus.

While we have lllustrated and described an apparatus adapted for use in the practical application of the method, it is to be understood that such apparatus may vary in character, form and operation, depending upon the individual re uirements.

he arsenate of lead pro need in accordance with our method is of a superior quality when produced from materials of suitable quality. It settles and is separated as a finely divided material of extreme subdivision. It' remains in suspension in a liquid such as water for extended periods, and is particularly adapted, in connection with a deflocculating agent, foremployment as an insecticide. When so employed and applied to vegetation, the arsenate is deposited in the form of fine particles or crystals which do not tend to aggregate, but, on the contrary, spread themselves uniformly over the surface to which the material is applied. N o nitric acid or other electrolyte is employed in carrying out the method and the product is substantially free from electrolytes.

The method as herein described is well adapted to the production of large quantities of arsenate of lead in a simple and advantageous manner.

We claim:

1. In the preparation of arsenate of lead,-

the improved method which comprises suspending finely-divided lead oxid in a liquid medium substantially free from electrolytes other than those resulting from the partial hydrolysis of the suspended lead oxid, and adding arsenic acid or oxid thereto in such a manner as to produce arsenate of lead in fine crystalline form substantially free from inapurlties and suitable for use as an insectic1 e.

2. In the preparation of arsenate of lead, the improved method which comprises suspending finely divided lead oxid in a liquid medium substantially free from electrolytes other thanthose resulting from the partial hydrolysis of the suspended lead oxid, heating said medium to a temperature of about 70 C. to 100 C. and adding arsenic acid or oxid thereto.

3. In the preparation of arsenate of lead, theimproved method which comprises suspending finely-divided lead oxid in a liquid medium substantially free from electrolytes other than those resulting from the partial hydrolysis of the suspended lead oxid, heating said medium to a temperature of about 70 C. to 100C. adding arsenic acid or oxid thereto, and agitating the mass.

4. In the preparation of arsenate of lead, the improved method which comprises suspending finely div-ided lead oxid in a liquid medium substantially free from electrolytes other than those resulting from the partial hydrolysis of the suspended lead oxid,

gradually adding arsenic acid or oxid'thereto and maintaining the temperature of the medium at a point appropriate to the desired reaction.

5. In the preparation of arsenate of lead, the improved method which comprises suspending finely-divided lead oxid in a liquid medium substantially free from electrolytes other than those resulting from the partial hydrolysis of the suspended lead oxid, gradually adding arsenic acid or oxid thereto, maintaining the temperature of the medium at a point appropriate to the desired reaction, and a itating the mass.

6. In the preparation of arsenate of lead, the improved method which comprises maintaining finely divided lead .oxid in suspension in water heated to about 70 C. to 100 C. in the proportions of about 1600 pounds of lead oxid to 2700 gallons of water, and gradually adding thereto adilute solution of arsenic acid or oxid until the hereinbefore described test with lead solution shows the presence of free arsenic acid, and subjecting the suspension to agitation during such addition.

In testimony whereof we hereunto affix our signatures.

OSCAR F. HEDENBURG. DAVID S. PRATT. 

